Nanometer measurement has become more and more important in the development of metrology, material science,
microelectronics and biology. Heterodyne Fabry-Perot interferometer can be used in the nonlinear error calibration with
an accuracy of nanometer and sub-nanometer order. We can get very high resolution by using heterodyne Fabry-Perot
interferometer frequency locking technique in theory. However, the measure uncertainty and the stability of results are
worse than the expectation's. In this paper, in order to solve the problems of air refrective index change and temperature
excursion, we designed the vacuum system that adjusts the interference light path and built it based on NIM's heterodyne
Fabry-Perot interferometer. The key in our design is to reduce the thermic balance time and to ensure reliable
hermetization of movable components. The influnce of the change of air refractive index to the measured precision was
studied, and the approximate formula of vacuum degree that the system requires was concluded. It has been proved in
the experiment that the system works steadily. The system's ability of anti-jamming has been improved, and the demand
of the measure surroundings has been lowered. Comparing with capacitance displacement measurement instrument, we
conclude that the nonlinear degree of this system in the range of 0.35um, which is longer than half of the wavelength of
the laser, is better than 3.9nm.